1. Field of the Invention
The present invention relates to a piezoelectric drive element equipped with drive electrodes, for cast printer heads used in ink-operated mosaic printer units, in which printing liquid is ejected droplet fashion by a mechanism of piezoelectric contraction of the cylindrical drive elements which surround the ink passages.
2. Prior Art
Piezoelectric drive elements for printing jets have been known for a considerable time now. An U.S. Pat. No. 3,298,030 discloses an ink-jet printer unit using as printing jet a small glass tube which is filled with printing liquid and is surrounded by a cylindrical, piezoelectric drive element. The drive element consists of a piezoceramic tube whose peripheral surfaces have been coated with metal by a vapor-deposition process and which is driven through said peripheral surfaces which function as electrodes. With application of an electrical pulse to the electrodes, the piezoelement and the internal glass tube tract with the consequence that an ink droplet is ejected from the tube.
If piezoelectric drive elements of this kind are combined in accordance with one proposal to form a mosaic printer head in which the individual drive elements are cast in situ in the head, special design problems are encountered in the drive elements as a consequence of the casting operation and of the small dimensions of the head, in particular problems of contacting each individual drive element and problems associated with its security against short-circuiting.
In mosaic printer heads of this kind, the drive elements comprise ink passages arranged in the printer head, the drive elements being in direct contact with the printing liquid. This means that the drive elements are exposed to the risk that ink will penetrate into the porous ceramic resulting in short-circuits thereat. Also, the thin electrodes applied to the drive elements, are extremely difficult to contact.